Inheritance is an abstraction that enables you to separate a class from one or more refined versions of the class. The refined versions of the class are called subclasses or derived classes. A subclass can be thought of as a "kind of" class. The class that the subclasses (or derived classes) refine is called the superclass or base class. The subclasses are connected to the superclass by an inheritance line.

When drawing an Inheritance Line on a Class Diagram, you must draw from the Subclass to the Super (base) Class. Once the Inheritance Line has been drawn, no changes may be made to it's direction.